prom vs exgirlfriend..

prom is tommorrow! i just got notice from like an ex-girlfriend (really never dated but real close) that she will be at the prom and would like to dance with me some. I still have feelings for this girl, because I really like her and her family, plus I have known her for like 5 years.

im worried because i dont know if I can dance with her because my current gf but I really want to just to see if a connection happens. she just broke up with her bf and all so im kinda scared and not sure what to do.